1. Field of the Invention
The present invention relates to a bearing device such as a hub unit for a vehicle comprising a shaft and a bearing and a rolling bearing mounted to the shaft body.
2. Description of the Related Art
Referring to FIG. 7, in a conventional hub unit, a double row angular contact ball bearing 82 with vertex of contact angles outside of bearing is fitted and mounted around a shaft portion 81 of a hub wheel 80. A free end of the shaft portion 81 is bent outward in a radial direction by rolling-caulking. The bent caulked portion 85 pushes an outer end face of an inner ring 84 of the bearing 82. With this pushing operation, the bearing 82 is fixed to the hub wheel 80 to prevent the bearing 82 from falling out from the hub wheel 80.
Before the free end of the shaft portion 81 is caulked, the free end has a shape of a cylindrical portion. This cylindrical portion is rolling-caulked using a caulking jig. With this operation, the cylindrical portion of the shaft portion 81 is bent outward in the radial direction to form the caulked portion 85 so that the inner ring 84 is prevented from falling out.
In such a hub unit, an entire outer surface of the inner ring 84 of the bearing 82 is subjected to hardening treatment. Therefore, in order to enhance a resisting force against the falling-out phenomenon of the bearing 82, it is necessary to set a caulking load stronger.
On the other hand, if the caulking load is excessively strong, a raceway surface of the inner ring 84 is affected and there is an adverse possibility that rolling characteristics of the bearing 82 is deteriorated. Therefore, it is necessary to set the caulking load appropriately.
Therefore, it is a main object of the present invention to provide a bearing device capable of appropriately setting a caulking load such that a raceway surface of an inner ring is not affected while a falling-out resistance of a bearing can be strengthened.
Other objects, features and advantages of the present invention will be apparent from the following description.
A bearing device of the present invention comprises a shaft body and a rolling bearing mounted around the shaft body, wherein the shaft body is provided at its free end with a caulked portion. The caulked portion is bent outward in a radial direction to push an end face of an inner ring of the rolling bearing, thereby preventing the rolling bearing from falling out. A raceway surface of the inner ring of the rolling bearing is subjected to hardening treatment, and other portion of the inner ring is made of raw material which is not hardened.
According to such a structure, the portion of the inner ring of the rolling bearing other than the raceway surface can be made of raw material. Therefore, the caulked portion formed by the caulking plastically deforms the relatively soft inner peripheral corner of the miner ring and as a result, the caulked portion and the end face of the inner ring are adhered to each other strongly without adversely affecting the raceway surface of the inner ring.
In the invention, preferably, the inner ring is made of high-carbon chromium bearing steel or carbon steel for machine structural use as base material, and its raceway surface is subjected to hardening treatment by induction hardening. The raw material portion of the inner ring is prevented from being excessively deformed by a caulking load at the time of caulking so that a stable structure can be obtained.